The present invention relates to nonlinear optical (NLO) materials, compositions thereof and NLO devices using those compositions. More specifically, the present invention relates to polymeric matrices supporting a second order NLO material defined by the formula (I)
EDxe2x80x94Bxe2x80x94EWxe2x80x83xe2x80x83(I)
where ED is an electron donating moiety, B is an aromatic containing bridging moiety, and EW is an electron withdrawing moiety (terminal acceptor group) defined by formula (II), 
where C1 is a carbon atom linked through a double bond to a cyclic or an acylic carbon atom in the aromatic containing bridging moiety, and A1, A2, A3 or A4 are the same or different from one another, each of which is an electron withdrawing group such as CN, COR, COOR, COOH or CHxe2x95x90C(R)2 where R is a C1-6 alkyl group. In addition A1, A2, A3 or A4 can also be a C1-8 alkyl group, C3-7 cycloalkyl group, or an aryl group, with the proviso that at least some of A1, A2, A3 or A4 are an electron withdrawing group.
Despite advances in the performance of nonlinear optical (NLO) materials, new NLO materials are still needed which provide particular advantages and combinations of properties. Such materials find utility in, for example, optical computing and optical signal processing. Although a variety of both organic and inorganic NLO materials are of interest, organic polymer-based NLO materials have attracted considerable attention. Relatively early NLO polymers are discussed in, for example, Nonlinear Optical and Electroactive Polymers (eds. P. Prasad and D. Ulrich; Plenum; 1988) and Introduction to Nonlinear Optical Effects in Molecules and Polymers (P. Prasad and D. Williams; John Wiley; 1991). An example of recent work is U.S. Pat. No. 5,414,791 (Ermer et al.) which describes the synthesis and testing of novel compositions for use in thermally-stable electrooptic waveguides incorporated herein by reference.
In particular, NLO compositions are needed which provide higher second order NLO effects. To achieve high second order NLO properties, both microscopic and bulk material considerations can be important. One important measure of the microscopic second order NLO effect is the molecular hyperpolarizability value xcex2 (beta). The above-noted text edited by Prasad and Ulrich notes (pg. 8) that:
A conjugated structure with an electron-rich (donor) group on one end and a deficient (acceptor) group on the other end contains the asymmetric charge distribution in the Π system requiredfor large xcex2. In addition to large microscopic beta values, however, large bulk second order nonlinear optical susceptibility "khgr"(2) is needed. The problem in achieving high "khgr"(2) is that materials which have large asymmetric charge distributions (i.e., high beta) also tend to have centrosymmetric order which reduces "khgr"(2). Several approaches have been developed, including xe2x80x9cpoling,xe2x80x9d to achieve the non-centrosymmetric order required for high "khgr"(2). Although a variety of material properties are important in the NLO arts, the general focus of the present invention is developing commercially viable materials with both high beta and "khgr"(2) values.
Numerous U.S. patents describe NLO materials include, for example, U.S. Pat. Nos. 5,414,791; 5,561,733; 5,718,845; 5,708,178; 5,776,374; 5,783,306; 5,804,101; 5,811,507; and 5,834,575. In addition, second order NLO materials are described by Sun et al. in Mat. Res. Soc. Symp. Proc. vol. 413, pp. 263-268 (1996) entitled xe2x80x9cSynthesis and Characterization of 1,3-Bis(Dicyanomethylene)indane (BDMI) Derived Second Order NLO Materials.xe2x80x9d
Despite these and other contributions to the NLO arts, a need remains for novel organic chemical structures to provide properties and combinations of properties not heretofore observed.
In its broadest sense, the present invention provides novel NLO compositions, device elements and devices which comprise the novel NLO compositions, methods of making and processing the NLO compositions, and methods of using the NLO compositions. Basic and novel characteristics of the present NLO compounds include excellent NLO properties.
One aspect of this invention is providing a compound that has both large microscopic beta values, as well as, large bulk second order nonlinear optical susceptibility "khgr"(2), where r33 values are greater than 25 pm/V.
Another aspect of this invention is providing a device having second order nonlinear optical properties by incorporating a chromophore defined by the formula (I)
EDxe2x80x94Bxe2x80x94EWxe2x80x83xe2x80x83(I)
where ED is an electron donating moiety, B is a bridging moiety, and EW is an electron withdrawing moiety (component) which is a terminal acceptor group defined by formula (II) 
where C1 is a carbon atom linked through a double bond to a cyclic or an acylic carbon atom in the bridging moiety, and A1, A2, A3 or A4 are the same or different from one another, each of which is an electron withdrawing group such as CN, COR, COOR, COOH or CHxe2x95x90C(R)2 where R is a C1-6 alkyl group. In addition A1, A2, A3 or A4 can also be a C1-8 alkyl group, C3-7 cycloalkyl group, or an aryl group, with the proviso that at least some of A1, A2, A3 or A4 are an electron withdrawing group.
Another object of the present invention is providing a second order NLO material defined by the formula 
where R1 and R2 can each be a C1-6 alkyl group, such as a methyl, ethyl, propyl, iso-propyl, butyl, iso-butyl, pentyl, iso-pentyl, hexyl or iso-hexyl group, or a C1-6 alkanol group, such as methanol, ethanol, propanol, butanol, pentanol or hexanol, or a (xe2x80x94CH2)nxe2x80x94CHxe2x95x90CH2 group where n=1, 2, 3, 4, 5 or 6. B is aromatic or pseudoaromatic containing bridging moiety defined by formula (V) 
where R3 is an homocyclic or heterocyclic aromatic group having 4 to 7 carbons atoms, wherein the heterocyclic atom is N, O or S, and the homocyclic or heterocyclic aromatic group is unsubstituted or substituted with a C1-6 acylic or cyclic alkyl group, such as an arylalkyl, a pyrrole, a furan or thiophene group, or the group R3 can also be cyclohexene substituted with a C1-6 alkyl group. In formula II, A1, A2, A3 or A4 are the same or different from one another, each of which is an electron withdrawing group such as CN, COR, COOR, COOH or CHxe2x95x90C(R)2 where R is a C1-6 alkyl group. In addition A1, A2, A3 or A4 can also be a C1-8 alkyl group, a C3-7 cycloalkyl group, or an aryl group, with the proviso that at least some of A1, A2, A3 or A4 must be an electron withdrawing group. Preferably R1 is ethanol, R2 is an ethyl group, and A1-A4 are each a cyano group.
Another object of the present invention is providing a polymer matrix containing at least one second order NLO material defined by the formula (II) 
where R1 and R2 can each be a C1-6 alkyl group, such as a methyl, ethyl, propyl, iso-propyl, butyl, iso-butyl, pentyl, iso-pentyl, hexyl or iso-hexyl group, or a C1-6 alkanol group, such as methanol, ethanol, propanol, butanol, pentanol or hexanol, or a (xe2x80x94CH2)nxe2x80x94CHxe2x95x90CH2 group where n=1, 2, 3, 4, 5 or 6. B is an aromatic or pseudoaromatic bridging defined by formula (V) 
where R3 is an homocyclic or heterocyclic aromatic group having 4 to 7 carbons atoms, wherein the heterocyclic atom is N, O or S, and the homocyclic or heterocyclic aromatic group is unsubstituted or substituted with a C1-6 acylic or cyclic alkyl group, such as an arylalkyl, a pyrrole, a furan or thiophene group. The group where R3 can also be cyclohexene substituted with a C1-6 alkyl group.
The Groups, A1, A2, A3 or A4 are the same or different from one another, each of which is an electron withdrawing group such as CN, COR, COOR, COOH or CHxe2x95x90C(R)2 where R is a C1-6 alkyl group. In addition A1, A2, A3 or A4 can also be a C1-8 alkyl group, a C3-7 cycloalkyl group, or an aryl group, with the proviso that at least some of A1, A2, A3 or A4 are an electron withdrawing group. Preferably R1 is ethanol, R2 is an ethyl group, and A1-A4 are each CN.